This invention relates to methods and systems for powering combustion apparatus with hydrogen.
As a result of recent shortages in hydrocarbon fuels and the recognition that the supply of such fuels will ultimately be exhausted, there has been an increased interest in finding and developing alternative fuels. One alternative fuel whose potential has long been recognized but, as yet, has not been fully realized is hydrogen. The attractiveness of hydrogen as a fuel lies in the fact that it is one of the most abundant of all elements, that conventional internal combustion engines can be readily adapted to operate on hydrogen and in such operation, unlike gasoline, a large percentage of the hydrogen is converted to power the engines, and that the burning of hydrogen in such engines can be made to be relatively pollution free. See, for example, U.S. Pat. Nos. 3,983,882 and 4,016,836. Of course, the potential of hydrogen as a fuel is not limited to internal combustion engines but also extends to industrial use, use in fuel cells and in home and mobile home heaters, and to any situation where natural gas, propane gas, etc., is presently used.
One of the problems which has thus far prevented the widespread use of hydrogen as a fuel has been the difficulty in efficiently and safely storing the hydrogen. Storing hydrogen as a liquid is costly since it requires considerable energy to liquify the hydrogen, and transfer of the liquid from one container to another results in a loss to the atmosphere of much of the hydrogen. Also, containers for the liquid hydrogen must be extremely well insulated to reduce the loss of hydrogen due to vaporization or boiling. Storing hydrogen as a gas requires extremely heavy and bulky containers and is impractical for most presently contemplated consumer uses.
The use of hydride material (hereinafter defined to mean any metals, metal compounds or other materials capable of absorbing or adsorbing and holding hydrogen) appears to be an attractive approach to the storage of hydrogen for consumer purposes. Exemplary hydride material includes iron titanium, misch-metal tetranickel, and columbium. Storage of hydrogen in the hydride material (sometimes referred to as hydriding the material) typically involves lowering the temperature of the hydride material and then applying hydrogen gas under pressure to the material. After the hydride material absorbs the hydrogen, the material is sealed in a container under pressure to maintain the material in the hydrided state until the hydrogen is needed at a subsequent time. Recovery or withdrawal of the hydrogen involves a process substantially opposite that used for storing the hydrogen, i.e., heating the hydride material and releasing some of the pressure of the container in which the hydride material is maintained.
As was discussed in U.S. Pat. No. 4,016,836, heat sources such as exhaust gases and engine coolant are present on most conventional internal combustion engines and so can be adapted to provide the heat necessary to heat the hydride material for hydrogen recovery. Utilizing, or even eliminating, existing accessory systems of a conventional internal combustion engine, of course, would provide significant cost savings.
Although use of hydrogen as the sole source of power is desirable in many instances for the reasons outlined above, there may be circumstances where it would be desirable to also have the capabilities provided by the use of hydrocarbon fuel as the source of power--for example, as an alternate fuel backup system, for operation in a region located a substantial distance from a hydrogen refueling depot, for extended range capability, when operating in areas which permit automotive exhaust pollution well in excess of the levels produced by hydrogen combustion, when one or the other fuel is less expensive, and when a higher power level is required.